New Publication: Land Use Drives Biotic Homogenization

Intensive use of grasslands by humans reduces species diversity and makes the landscape more monotonous, so that the same species end up everywhere. Nature is then no longer able to provide us with many essential ‘services’, which range from soil formation for food production to pest control. Led by the Technical University of Munich (TUM) and the University of Bern, 300 scientists studied the consequences of land-use intensification for biodiversity at the landscape level and for the first time could do this for a wide range of species groups. The results of the study are published in the scientific journal “Nature”.

Normally, every meadow is different, with varying species finding a suitable habitat in different places. However, when grasslands are used very intensively by people only a few plants and animals can survive and this is the catalyst for an increasing loss of species. In previous studies, this effect was shown for particular groups, such as birds, within a particular habitat. But would land use not have a much greater effect on species loss if it were studied on a larger spatial scale and if the full diversity of life — from single-celled organisms to vertebrates — were included? 

With this question in mind the scientists analysed and evaluated a unique data set. For the very first time, the study provided evidence that intensified use led to all grasslands across regions becoming similar and only able to provide habitats for a few species, a process known as "biotic homogenization".  

The data used in the study come from the DFG Biodiversity Exploratories that comprise three areas, including the UNESCO Biosphere Reserve Swabian Alb, the Hainich National Park and its surroundings, and the Biosphere Reserve Schorfheide-Chorin. All three regions differ in terms of climate, geology, and topography, but are managed by farmers in a manner typical for Europe. More than 4,000 species were analysed using an innovative statistical procedure. This new method allowed the researchers to test where biotic homogenization occurs most strongly, along a gradient of land-use intensification. 

A unique feature of the study was that data from organisms in the soil such as bacteria, fungi, and millipedes were also included. The species were subdivided into twelve groups according to their position in the food chain, and whether they live above or below ground. For example, one group of above ground species is that of the primary producers, mainly plants. Other groups include herbivores and plant pollinators, as well as their predators.   

The findings showed that it did not matter whether grasslands were used moderately or intensively by humans. “This emphasizes the importance of carefully-planned, low intensity management of grasslands for biodiversity conservation,” said Dr. Sasha Keyel, formerly with the Faculty of Forest Sciences and Forest Ecology at the University of Göttingen and now at Colorado State University. Only grassland areas that are managed extensively provided suitable habitats for more specialized species and are therefore essential for protecting species diversity. Moreover, the decline in species diversity also results in fewer interactions between individual species. “If biotic interactions get lost, the functionality of ecosystems will be affected. Changes in pollination or biocontrol services may reduce agricultural production and hence impair human well-being”, said Dr. Catrin Westphal from the Agroecology group at the Georg-August-University Göttingen. “So, only when as many species as possible are able to find the unique habitats they require across large areas multiple ecosystem services can remain intact”, added Prof. Dr. Teja Tscharntke head of the Agroecology group.